1. Field
The present invention is related to solar energy generation and storage and, in particular, to a personal solar appliance for generation and storage of solar energy.
2. Discussion of Related Art
Solar cells or photovoltaic cells can be considered large area semiconductor diodes that convert sunlight into electrical current, which is used to produce usable power. The output power of the solar cell depends on multiple factors such as sunlight intensity, temperature, orientation of the cells with respect to the sun, and efficiency of the solar cells.
Photovoltaic systems, using solar panels, directly convert sunlight into energy using the principles of the photoelectric effect. The photoelectric effect takes advantage of the properties of semiconductor materials, with silicon being the primary material used in photovoltaic solar cells. When photons strike the solar cell, electrons in the semiconductor material are freed and allowed to flow as electricity. The direct current (DC) electricity produced can be directly used to charge batteries. The DC current can also be coupled to an inverter to power alternating current (AC) components or the AC current be connected to a local electrical power grid.
Traditional photovoltaic systems are based on silicon. Silicon ingots are sliced into wafers that are fabricated into cells. Cells are combined into modules, which are packaged into end-user systems. Silicon-based solar cells typically have efficiencies up to about 18%. Semiconductor materials, like gallium arsenide, have efficiencies that approach 40%, but are much higher costs than silicon. Gallium arsenide, therefore, is not currently economically practical for many terrestrial applications and is used for the most part on spacecraft and interplanetary robots. Thin film technologies use a variety of semiconductors but their efficiency is typically less than 10%.
A battery charger is a device used to put energy into a rechargeable battery by forcing an electric current into the battery. The charge current for a battery depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 volt car battery (several Amps) will be very different from the current that should be applied for recharging a mobile phone battery (e.g., 250 mA to 1000 mA). However, solar cell output current can be utilized to charge any battery.
In many areas, especially where electrical power is unavailable or unreliable, there is a need for devices that are capable of powering user devices such as lights, radios, MP3 players, cell phones, or other devices, or are capable of charging batteries directly.